NASA officials say astronauts will delay a spacewalk planned for Thursday until Friday, August 6. The space agency says flight controllers and station managers made the decision late Monday night to postpone the spacewalk after reviewing proposed timelines. The astronauts will replace a failed ammonia pump on the International Space Station. A second spacewalk to complete the repairs is planned for Monday.

Many people on Earth have experienced this scenario: One minute, all of your electrical appliances are functioning well and the next minute something trips a circuit breaker. It can happen in space, too. And it is more challenging to fix.

NASA says a cooling pump failed on July 31, after a spike in electrical current tripped a circuit breaker. That pump feeds ammonia into cooling loops to maintain the proper temperature for the station's electrical and flight systems. When the pump failed, it shut down half of the space station's cooling system. Meanwhile, another pump continues to function properly.

Astronauts already had plans to conduct a spacewalk on Thursday, which, in space parlance, is called extravehicular activity, or an EVA. Now the spacewalk will focus on replacing the broken pump. Astronauts Doug Wheelock and Tracy Caldwell Dyson will remove the failed module and install one of four spares.

The pump failure forced astronauts to switch off some equipment to reduce the amount of heat on board the International Space Station, or ISS.

Program Manager Michael Suffredini told reporters that all critical operations, and some lesser ones, could continue at current levels.

"Really, from an ISS perspective today, we're in fine shape," said Suffredini. "We're just trying to make sure we get the EVA done before we suffer the next failure in that system, which, while very unlikely, is something we ought to do as a program to make sure we give ourselves the best chance of success."

Suffredini says ISS crew members have trained for some maintenance and repair operations, and that this is one such mission.

Flight Director Courtenay McMillan, who will lead the team supporting the spacewalks, told reporters that NASA usually allows two weeks to prepare for such tasks. But in this case, she says, astronauts will have only a few days to map out the repair operation.

"We decided to take advantage of the fact that the crew already has the airlock and all the suit systems all ready to go," said McMillan. "But this is a very aggressive timeline for us to get the procedures ready."

McMillan says the astronauts will have to move a 350-kilogram module. "It is very big and, like I said, it's unwieldy to maneuver. So a lot of the maneuvering is going to require a second person either to kind of spot and watch where they're going or to actually assist with the maneuvering. So it's going to be a tricky choreography for the two crew members to do."

NASA officials say the six crew members aboard the space station are not in danger. They say the crew has changed focus, so instead of carrying out research, the astronauts are prepping for the repair work.